With broad utilization of integrated circuits, the reliability of conductive connection becomes increasingly important. Among corrosion and electromigration, stress-induced voiding is one of major causes resulting to the malfunction of integrated circuits on chips. The reason is speculated to be that small notches usually originate at grain boundaries and migrate slowly towards low-stress region according to stress gradient to relieve the stress. Along the time, small voiding distributed in conductive material such as metals grows, moves, and accumulates in low-stress regions. As a result, stress-induced voiding causes discontinuities in conductive connections of the integrated circuits. The discontinuity results in open circuit failure in one layer metallization structures and an increase in the line resistance in the metallization structure formed by multiple layers of refractory metals such as W, TiW, Ta, TaN, and Ti.
Void growth is governed by some variables such as the properties, microstructure, and processing of the metallization. The circuit failure by stress-induced voiding depends upon void morphology such as size, shape, and density of voids and the geometry of the metallization. Voiding becomes a serious problem in particular in narrow aluminum lines. Some approaches are employed to improve the stress-induced voiding phenomena such as using copper and other additives as alloying elements, reducing contaminant concentrations like nitrogen and oxygen, and producing metallization films with larger grain sizes.